Winding for electric furnaces



Oct. 14, 1930. 1,77 8,398

E. F. ,NORTHRUP WINDING FOR ELECTRIC FURNACES Filed June 5, 1928 'fatented @ct. M 193@ rates EDWIN FITCH NORTHRUP, 01E PRINCETON, NEW JERSEY, ASSIGNQ L T AJAX ELECTPJU- THERIMIC CORPORATION, OF AJAX PARK, NEW JERSEY, A CORPORATIQEQ (SF NEW JERSEY WINDING FOR ELECTRIC FURNACES Application filed June 5,

My invention relates to the art of inductive electric furnaces in which there is danger of leakage of molten metal through the furnace refractory.

5 One purpose of my invention is to automatically give warning or cut off the power supply when the molten furnace content has broken through the refractory about it to any predetermined extent.

A further purpose is to give an alarm or tocut off the power supply from the inductor coil of an induction electric furnace when leakage flow of molten metal has altered the condition of an electric circuit by which the furnace is protected.

A further purpose is to provide a protective electric circuit about the side or bottom walls retaining a mass of molten metal, or about both in such relation that penetration of 29 the molten metal through the refractory as far as the circuit will short-circuit or open this circuit, thereby giving an alarm or shutting off the power from the furnace.

A further purpose is to protect the inductor coil of an induction electric furnace and to protect the operators from injury by molten metal breaking through from the molten content.

A further purpose is to introduce a protective electric circuit between the metal and the inductor coil of an electric furnace with heat insulation on both sides of the circuit as a means of giving warning or checking the flow of electric current through the furnace when the melt has started to leak through the refractory.

A further purpose is to provide an lectric circuit surrounding'a pool of molten metal with a balanced outer circuit which is unbalanced by the effect of the molten metal and when unbalanced gives visual or audible indication or shuts off the current for protection of the furnace.

A further purpose is .to provide an electric circuit which protects a furnace from leakage damage with an outside circuit having indicators distributed in different parts of the circuit indicating short-circuit or open circuit or normal condition of circuit.

1928. Serial Efio. 283,035.

Further purposes will appear in the specification and in the claims.

My invention relates to the method or processes involved as well as to apparatus by which they may be carried out.

I have preferred to illustrate my invention by variations of one main form only among many forms in which it might appear, selecting a form which is practical, ei'iicient, simple, reliable and inexpensive and which at the W same time well illustrates the principles of my invention.

Figure 1 is a vertical central section over a water-cooled inductor furnace, having a protective winding capable of carrying out my invention.

Figure 2 is a vertical central section through an air-cooled inductor furnace, showing a slightly different arrangement of the protective winding. 79

Figure 2 is a fragmentary section similar to Figure 2, showing refractory only and varying slightly from Figure 2.

Figure 3 is a diagrammatic illustration of an electric circuit including a protective winding.

Figure 4 is a diagrammatic view somewhat similar to Figure 3, but showing a different arrangement of indicators or current interrupting mechanism in the circuit.

Figure 5 is a diagrammatic View applying Wheatstone bridge connections.

Figure 6 is a diagrammatic view applying lVheatstone bridge connections with a current interrrup-ting mechanism.

In the drawings simliar numerals indicate like parts. i

In all furnaces handling molten content and'in all refractories holding molten metal the refractory progressively deteriorates. For this reason as well as because of occasional breakage of solid refractories there is constant danger of leakage of the molten metal.

While my invention is therefore of value in all such furnaces it finds its greatest need and hence its greatest utility in electric furnaces of the induction type free from interthreading of transformer iron and in which the inductor surrounds the furnace pool.

In such furnaces it is necessary to have the diameter of the metal as large in roportion to the total diameter of the coil interior as.

possible to improve the coupling. The necessity for close coupling between the pool and coil reduces the spacing for refractory to a minimum, increasing the danger of short circuiting of the coils by leakage of the metal.

This short-circuiting may be highly injurious to the-inductor coils even with aircooled'coils, but in the case of water-cooled dangerous both to the operators and to the ap- I -paratus.

Y exploring circuit.

. I find that complete protection can be obtained against failure of insulation by cutting of the power input, or partial protection may be had by warning, for any predetermined extent of failure of insulation and consequent leakage at any point or over any area desired. I secure this protection by locating an exploring winding about the fur.- nace or within the refractory where protection is desired, usually covering by the wind-v ing the entire space between the molten metal and the inductor coil to fully protect the latter, or I may completely surround the sides and bottom of the molten metal pool if desired. t When the invention is applied to a furnace having a pool-surrounding inductor coil my invention contemplates protecting the lateral sides and if desired also the bottom of the electrio furnace pool by an exploringcoil connected in an electric circuit, so that leakage of molten metal beyond the confines of the pool toa depth determined by the spacing of the exploring coil from the molten metal will cause alteration in thecharacteristics of the The open circuit or short circuit produced is used to operate an alarm or relay, permissibly warning of the danger orcutting off the energy supply from the furnace or both.

As will be seen, the broad invention is independent of the character of the exploring coil, of the nature of the connection bywhich signal operation or power interruption is secured, and of the. detail ofthe furnace itself. It is my understanding'that ,I am the first to make use of an exploring coil for any such purpose in any furnace and that I am the first to protect against refractory failure electrically byany signal, alarm or supply current interruption. For the above reason in applicationto the broad invention I have intended my drawings to be diagrammatic and illustrative merely of structure by which my invention may be carried out. In so far as I have shown furnace structure at all, I have chosen my illustrations for the purpose of making my meaning more clear and not with ing a crucible 12 surrounded by a watercooled hollow inductor coil 13 whose electrical connections are shown at 14, 15 and whose water-cooling inlet and outlet connections are shown at 16 and 17 respectively. Within the water-cooled furnace inductor coil 13 I provide a protective cylinder 18, which is desirably strong enough mechanically and heat resistant enough to stop a flow of molten metal directed toward the coil unitl an electric alarm can be answered or until automatic cut-off of the current from the inductorcoil will have been effective to chill the furnace and to thus retard or stop leakage flow of the molten metal.

This protective cylinder 18 may be the regular cylinder which electrically insulates the inductor coil or a special cylinder, of any suitable material and desirably extends to a point below the inductor coil. It may seal at the bottom with a sand or other suitable base for the crucible or with a bottom for the melt where no crucible is used. Between the cylinder 18 and the melt I. provide sand or other heat insulation desired. Here the melt is illustrated as lying within a crucible. Within this space I mount my exploratory coil, loop or other screen winding it non-inductively where the furnace has an inductor coil but otherwise without the same need ofcare in this particular. The source of current can be'direct or alternating and of any voltage for which the circuit is suited; The winding can be of insulated or uninsulated wire.

1 With additional heat insulation a choice of location is offered and the coil, as my screen "will be-called for convenience, may be located" along the inner surface of the heat insulation, along its outer surface or within the body of or between parts of the heat insulation,

depending-upon the distance from the crucible at which it is desired to have the exploratory coil operate and upon the question of how much protection against further flow of molten metal isto be provided in the direction of its flow and beyond the exploratory coil- I find that it is quite convenientto mount the exploratory coil upon a cylinder or frame 19 which may itself form a part of the heat and electrical insulation. "The wires of the masses coil may be separately insulated or may take their insulation from the cylinder 19.

In Figure 1, as suggested the exploratory coil is not desirably wound inductively because in that Case current will be induced in it and therefore in its circuit from the main inductor coil as a primary'in excess of the current which should be needed for this circuit, reducing the eliiciency of the main inductor coil and at the same time defeating the purpose of the exploratory coil by the excessive current flow in the circuit of the exploratory coil. The exploratory coil is therefore wound non-inductively wherever induction would occur. Tt is wound differently in the forms shown in Figures 1 and 2 and may, obviously, be wound in many other different ways.

In Figure 1 the coil comprises a length doubled upon itself to form a loop 21 and 22. The two sides are wound side by side around the support or cylinder 28, in ring form producing a winding much like that of a Gramme ring. The distance between adjoining double wires 24 is small enough to prevent flow of any appreciable amount of leakage molten metal between one loop pair and the next without opening the circuit by melting the wire or causing a short circuit between the adjoining portions of the double winding.

The otherwise open ends of the double winding are connected to a source of energy through an indicator or relay, so that either opening the circuit or short-circuiting the wires of the coil will operate an alarm, if alarm only be desired, or will cut off the current from the inductor coil of the furnace so as to prevent further injury to the in ductor coil or to the individuals or apparatus about it.

In the form shown in Figure 2, the inductor coil 13 is air-cooled, the furnace is of slightly different form and thc exploratory coil is differently wound.

The air-cooled coil 13". is free from the danger of explosion present with the water cooled coil but still presents the same danger to supply apparatus in case of short-circuit ing.

The difference in the furnaces is shown deliberately for the purpose of emphasizing the fact that the use of a crucible or the non-use of a'crucible, makes no difference in the application of my invention. The pool 11 here lies within an internally sintered refractory 20. The lining is effected by the initial use of a protective cylinder corresponding in outside diameter with the inside diameter of the furnace wall 21 and covering it outside and filling it in at the bottom with a suitable sand or resting it upon a sand bottom so that sintering takes place before destruction of the protective cylinder, leaving a sintered surface at 21 and at the bottom 22, which is efiective to hold the melt.

It is not my intention to claim this method of production of the lining form here.

The winding 23, 2% is non-inductively wound about a cylinder 18 outside of the refractory lining'and between this refractory lining and the inductor coil.

Tn Figure 2 the winding 23, 24 is shown as located within the refractory and as protecting the bottom as well as the sidesa protection which is easily added but which will ordinarily not be required because it is needed less and can be provided easily in other The refractory o Figure 2 may be a solid refractory as in Figure 1, within which the winding is encased during manufacture, or a loose refractory as in Figure 2. T have illustrated temporary means only for supporting it as in either case it would be supported by t 1e refractory. Tn principle it would *lCt matter whether the ten porary support ha out during baking of tl the furnace or remains in.

Tnstead of a Gramme ring winding as seen in Figure l, the windings in Figures 2 and 99 are helical windings having vertical axes.

l here it is desired to protect the inductor coil only, as where other forms of protection for the bottom are available, such as lealra claimed by me in another application, or are not regarded as necessar no exploratory coil protection for the botton is provid Where such a protection'is desired it is et. secured in any form by continuin end of the non-indnctive helical in the form of a doubl pancake spir or beneath the bottom refract r ure 2 he winding is placed within tory where it is desir-el coil shall give warning shut off the current wit metal through a part only 'ractory, as dieting f throu h substantiall the en need not be a coil in the usu acceptance that term but can be any systei networl arrangement of. conductors which covers not too great intervals the areas to be protected and which will reliably var in resistance sufficiently for operation of an indica- 1 o tion or a relay-when molten metal approaches V it or flows upon it. T recognize also that a refractory-encased exploratory winding can be encased within a loose refractory or within a solid refractory, baked or otherwise, such,

for example, as a crucible.

Whatever the form of application of the exploratory winding for the furnace, it istne intention to connect it with an outside circuit 27 including a source of energy and an "33o cator or indicators, or a relay or other operating mechanlsm, so that short-circuiting or opening the circuit or a considerable change of resistance of the circuit containing the current interruption are all protective devices for the furnace though the latter only is automatically corrective.

Not only may the forms of furnace and the exploratory winding or screen used with it be greatly variedas indicated, but it will be obvious that the variety of types and arrangement of protector whether indicator or current-interrupting mechanism may also be greatly varied to render the variation in exploratory winding resistance effective for the purpose indicated.

Among the many arrangements of circuit which would be effective with the type of exploratory windings shown I have illustrated four diagrams only of external circuit arrangements.

In Figure 3 the two sides of the loop' ex ploratory winding are shown as comprising the two sides 25 and 26 of circuit connected to a line 27 or other suitable source of current of any desiredvoltage, direct or alternating, generator or battery. The circuit is shown as containing a signal of one character or in one position such as a red light 28in series with one of the sides and a signal of another character or in another position such as a white light connected in series between the two sides.

With the connection shown the source of current is such that in normal operation both lights burn dimly. In case of short circuit as diagrammatically indicated at 30, through a flow of molten metal or because of heatcharring of insulation by the molten metal, the red light will burn brightly and the white light will go out.

On the other hand if the circuit be opened,

due, for example, to melting, of the conductor, as at 31 both lights will go out. It will be noted that in either event abnormal conditions cause the current through signal 29 to fail so that evidently a single signal at this point will sufiice; since it matters little whether the circuit be open or be short-circuited. This signal may be visible, audible, tangible or otherwise sensitory. Moreover,

was seen in Figures 4 and 5 it could be replaced by an' operating mechanism for an inductor-coil-circuit disconnecting switch.

- It is obvious that this is but one of many arrangements for grouping signalling devices so as to indicate abnormal circuit conditions. v In the form shownfiii Figure 4 the ends case however through coils. This reversal is intended to maintain substantially the same length of winding within the circuit in case of short circuit, wherever that short circuit take place avoiding possibility of but slight variation in resistance if short circuit take place near the ends of the winding parts.

The double windings are used to avoid induction and need not be used where no other winding is used which could cause objectionable induction. 7

I insert a resistance 32 in series with one of the double windings to insure that there will be a predetermined resistance in the circuit in the case of short circuit. I connect the two sides of the source of current through a coil 33 preferably engaging the resistance 32 at an intermediate point and connect the ends A and B through a coil 34. The coils 33 and 34 may comprise oppositely operating coils of a differentially wound elec tric magnet which will operate a signal of any character such as is shown in Figures 3 and 5 or will operate a galvanometer indicator to close a relay circuit at opposite ends of its stroke or will operate or release a shutter to energize a relay circuit, using the relay for signalling purposes or for interruption of the main power supply. I have not considered it necessary to illustrate the signal or relay operation further because of the illustration of signals in Figures 3 and 5 and of relay current interruption in Figure 6.

In Figure 5 opposite ends of the two parts of the double winding are connected in series to form an unknown resistance 39 in series with any indicator or relay shown here as a white lamp utilizing the double winding and protective device as one leg of a Wheatstone bridge 29 whose other legs are represented by resistances 30, 31 and adjustable resistance 32. The place of the galvanometer of the usual form of the Wheatstone bridge is taken by asecond protective device here shown as a red lamp. Any change in the resistance of the protective" exploratory winding, either by opening the circuit or by short circuit of any part of it will show itself to the operator by variation in the indication of one or both of the protective devices.

As in Figure 4, the reason for the connection of the opposite ends of the two conductors forming the doublewinding of the exploratory coil lies in the desire to make short circuiting efiective as much as possible, 1 as otherwise in case-of short circuiting close to the ends of the loop the effect upon the protective devices might be very slight and would require excessive delicacy of setting of the Wheatstone bridge. 1

course the difference in indicator is only one of many difi'erences which might be made in the application of this invention even Where a balance system is to be used and a change in a predetermined current flow or the unbalance oi this or oi any other balanced system could be used to open the circuit oi the main power supply. This is seen in Figure In Figure 6 the place of the white lamp is taken by a solenoidal winding so effective upon an armature ll to hold a switch lever 4:2 in an intermediate position. The lever is pulled in opposite directions by springs and e l. .ihe armature connects with the lever by a linlr d5.

the neutral position the switch connects between terminals as and i? of a relay circuit energized by o cry s8 and including a solenoid l9 which lifts armature 50 connected with a contact plate 51. l' hen lifted the contact plate engages and closes terminals 52 and ot a main Eurnace circuit containing a generator 5%., furnace coil 55. The power tacto is corrected by capacity 56.

Variation of the current through solenoid l0, either to increase it or to decrease it will cause interruption of the relay circuit and hence of the main furnace circuit.

it will be obvious the voltage of supply which may be necessary or advisable and the character or source of current are not material. ln-igure 5 ave intended to indicate this by showing resistance 'for the purpose of cuttin down a supply of current of too high vo e that voltage which may be desired L513 purpose.

lo view of i: y invention and disclosure variations and 1 whim or p: conic evident to others slrilled in the art, to obtain part or all of the benefits of ny invention without copyin he structure shown,

there-fore, claim. all such in so as and I cy tall wi run the reasonable spirit and y invention scope of n iaving thus described my invention wh I claim as new and desire to secure b Letters atent is 1. in a furnace, a. refractory holding molten metal exploratory electrically conductive windingabout the molten metal. an electric circuit connected with the winding and a protective device in said circuit operative with alteration or" resistance in the circuit due to refractory failure and molten metal efiect upon the exploratory Windin 2. In an electric furnace, a refractory adapted to contain molten metal, a furnace V winding surrounding a part of the molten metal, an electrically-conductive protective winding between the furnace winding and the molten metal and, an electric circuit including said protective winding altered in retively wound exploratory winding about sistance for protective purposes by flow of molten metal due to refractory failure.

3. ln an electric inductor furnace, a refractory adapted to contain a furnace pool. an inductor winding about the pool, an ex loratory winding betweenthe molten metal and the inductor, a source of energv in circuit with said winding and electromagnetic protective means operated by said circuit for protecting against lealrage of molten metal past the windin I l. In an inductor electric furnace, a refractory adapted to hold a furnace pool, an ductor coil surrounding; the refractory, an exploratory windin between the pool and the coil adapted to be short-circuited or opened by reason of failure of the refractory. a circuit includinu the winding, a source of current in said circuit and a protective device in said circuit adapted to operate by reason of variation 01- current flow in said circuit due to iei'ractor failure.

5. in an inductor electric furnace. refractory adapted to hold furnace pool, an in ductor coil surrounding the retractcry exploratory winding; between the pool an the coil adapted to be short-circuited 0" opened by reason of failure of the a circuit including the winding. so ce of current in said circuit and signal ing o rupting means operated by signalling or opening" the i supply with variation in so 6. in an induction :36 11 fractory adapted to hold metal, a liquid-cooled inductor coil ing said pooh a protective windin the pool and coil located within tcry, a circuit includi; the win Protective device cui' with var ation in. winding circuit.

In an induction electric furnace. refractory adapted to hold a cool of molten metal. an inductor coil surrounding said oo a non-inductive otective the pool and on i tory a circuit c a protective device in said circuit of with variation in the current throu winding circuit.

8. in a furnace a refractory.

uhe refractory. an electric circuit connected the coil and a protective device in said circc operative with al ation of resistance in e circuit due to reiiactory "failure rnolt metal effect upon the refractory winding.

9. In an electric furnace, a adapted'to contain molten metal, a furnace winding surrounding a part of the molten metal, a protective winding non-inductively wound between the furnace winding and the molten metal and a circuit for said protective winding altered by alteration of the resistance of the protective winding for protective purposes.

10. The process of protecting an inductor coil from injury by molten metal enclosed within it which consists in normally maintaining a flow of electric current at mterval points across the space between'the pool and the coil and in causing a variation in said current to give warning of refractory failure orflstop the flow of current in the inductor co 11. The process of warning or stopping the 1 current flow in an inductor circuit with failure of insulation about a furnace pool within the inductor'which consists in causing flow of molten metal due to refractory failure to vary an electric current and indicate the injury or stop the inductor; current flow.

12. .The process of protecting against fail-- ure' of refractory about molten metal which consists in utilizin the flow of the metal it-- self with partial failure of refractory to indi cate the failure of the refractory by variation of electric current.

v EDWIN FITCH NORTHRUP, 

